1. Field of the Invention
The present invention relates to an ignition system for an internal combustion engine, and particularly to a multiple-spark ignition system for igniting the fuel in the engine by multiple electric ignition sparks each ignition timing.
2. Description of the Related Art
P2003-521619A (WO01/055588) discloses a multiple-spark ignition system, in which a switching means is turned on or off according to the amount of the primary current flowing from a battery through the primary coil and the amount of the secondary current (discharging current) flowing through the secondary coil of an ignition coil. In more detail, the switching means turns off to generate multiple ignition sparks at a spark plug when the amount of the primary current increases to a threshold value, and turns on to start charging electric energy in the primary coil when the amount of the secondary current decreases to another threshold value.
However, if the battery voltage fluctuates when the primary coil is charged, the charging time of the primary coil varies. If the charging time increases, a ignition-less period in which the ignition spark is not generated increases, resulting in that the fuel ignition performance gets worse.